Dendritic cells (DCs) play a key role in the immune system as initiators of primary T cell responses. DCs are difficult cells to isolate because they are sparsely distributed in the tissues, and because there is a lack of positive markers identifying the cells. There is, thus, little information concerning DCs in various organs, and, while various researchers have postulated on the origin of these cells, it is not definitively known whether these cells constitute a separate lineage of cells. Furthermore, while there are many theories regarding this, it is not known if there is a dendritic committed progenitor cell in the bone marrow. The importance of solving these questions has become evident from a clinical perspective, as their function has made them into critical targets for vaccine development against tumor cells, and, potentially, in the development of vaccines against HIV infection.
Furthermore, since some DCs have been observed to serve as reservoirs for the HIV virus, identification of subtypes of cells having differences in infectability potential and/or the ability to provide infection resistance, is becoming increasingly desirable. In addition, there is considerable interest in identifying subsets of DCs believed to be involved in the induction of donor-specific tolerance after transplantation. Thus, there exists a need for methodologies to characterize and isolate dendritic cells.
Such methodologies would also be useful in the isolation of DCs by utilization of the phenotype by use of cytometry. Flow cytometry is particularly useful in this regard, as the cells bearing a particular phenotype can be recognized and sorted by use of labeled antibodies. Thus, DCs of a known phenotype could be sorted and isolated.